A conventional locating system makes use of satellite geo-locating receivers of the global positioning system (GPS) type or the like (GLONAS, Galileo, . . . ) fitted to the communications units of members of a group. Such GPS receivers serve to locate each member of the group in a terrestrial reference frame using their latitude, longitude, and altitude. The communications units can transmit their positions by radio, and can thus inform a coordinator of their respective positions. That system nevertheless presents the drawbacks associated with GPS technology. Specifically, it can be made inoperative or inaccurate as a result of environmental factors such as thunderstorms, high levels of humidity, or radio interference. GPS receivers can also be inoperative in covered sites such as in buildings or in underground installations. Since the deployment time for obtaining a location by GPS is associated with the time the GPS receiver requires in order to receive signals coming from satellites in sufficient number to enable the receiver to determine its position, several minutes may elapse before a unit can be positioned. Finally, the degraded accuracy of GPS for non-military uses can be found to be unsuitable for certain actions that require precise locating within a building, such as actions by emergency crews during a fire.